Industrial Control Wiring 1

[ejgreen]

When hooking up a stop/start station, is there a code that says that all equipment must have a stop cycle pushbutton and an emergency stop push button or can an emergency stop button be used for all stop procedures beside lock out procedures?

 

[waross]

Function is often a determining factor.
The service stop normally stops one piece of equipment.
The emergency stop stops everything.
The service stop is generally on a machine adjacent to the start button and other controls.
The emergency stop may be centrally loacated.
For a single machine, with an easily accessible control location if the service stop meets the requirements for an emergency stop I can see no reason that it can not serve as the emergency stop.
But it has been a few years since I have designed or installed control systems.
The codes may have changed with new requirements.
What is the wording of the code that you are working to?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ejgreen]

I don't know of any code that states any law. I have just heard both sides that for every emergency stop you should have a momentary stop. Just wasn't sure if there was a guideline to this or not.

 

[jraef]

Because "Emergency Stop" can mean different things in different systems, it's not a good idea to get your operators used to using an E-Stop button as the "normal" way to stop something. Inevitably they will learn that "it's the same thing" and use an E-Stop somewhere that causes consequences.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[IRstuff]

One might imagine that an E-Stop might be tied to alarms of some sort, while a maintenance stop wouldn't be.

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[FacEngrPE]

The E Stop needs to take the entire system to a "Safe" condition. Define safe. It is not the same as Safety Lockout for maintenance.
The stop button creates a different safe condition that might leave some parts of a machine in a "running condition".
Sometimes a you need to do a HAZOP to figure out the definition of safe for a particular operating system.

Mushroom buttons can be ordered as momentary contact, and in several varieties of locking buttons. While mushroom buttons are often used as emergency stops, I have seen pull cords and some other approaches. Not every mushroom button is an estop.

Operators need to understand their equipment - despite it not being cool - READ THE MANUAL. and when you are the designer explain safety aspects of your system in the manual so the operator and maintainer can understands.

This page

https://en.wikipedia.org/wiki/Kill_switch

indicates Directive 2006/42/EC. provides some guidance applicable to the EU. In the US start your research on OSHA's website for equipment similar to yours.
Fred

 

[che12345]

Dear Mr. ejgreen

Q. When hooking up a stop/start station, is there a code that says that all equipment must have a stop cycle pushbutton and an emergency stop push button or can ....".
A. There may be different practices/Standards/Regulations/Law in different parts of the world. In general, my observation is:
a) in most cases, the equipment is wired with "Start Stop" or "ON Off" push-buttons. Usually, the "Start" push-button is with a (spring loaded)* [NO]=normally open contact block while the "Stop" push-button is with a (spring loaded)*[NC]=normally closed contact block. The [colour code and size] varies in different parts of the world. Take note that the contact is (spring loaded)*, i.e. a NO contact changes status from (Open) to (close) when "pressed" and it [springs back automatically] to (open) position when the pressure is released=un-pressed. But, a NC contact changes from (Close) to (Open) when "pressed" and returns to (Close) automatically when "un-pressed". This is the set of push-button intended for "normal" routine starting and stopping operations.
b) in ALL cases, when an equipment is installed with an "Emergency stop" push-button; it is intended to be [tapped] to [STOP the equipment immediately] under "emergency" situation!. It is NOT intended to be used as a (normal routine) "Start Stop" , see above a).
This "Emergency stop" push-button may have a NO or NC contact block or with (NO + NC) blocks. Attention: the "Emergency stop" push-button is NOT (spring loaded)*. The contact does NOT reset once [tapped]. Reset is done MANUALLY by (pulling or twisting the mushroom head). The colour and mushroom head size may vary in different parts of the world. In the IEC world, the mushroom head is in RED and the big size labeling plate in AMBLE .
c) Depending on the (local regulation/Law ...) and the (type of equipment/system), [NOT all] equipment (MUST be installed with an "Emergency stop" push-button).
Che Kuan Yau (Singapore)

 

[ejgreen]

Thanks everyone for the input.

 

[itsmoked]

In some cases E-STOP can be used as The Stop. I prefer when it can be as that tests it's function many times a day. Sadly that's a minority of applications.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[che12345]

Dear Mr. itsmoked,

I. " In some cases E-STOP can be used as The Stop. I prefer when it can be as that tests it's function many times a day. Sadly that's a minority of applications ".
C. It is my (personal opinion) that your (personal preference/opinion) is not in line with the [international opinion/norm per IEC or NEC . They are for different functions. A on off push-button may be operated numerous times a day but not the emergency, " as tests it's function many times a day". As you also acknowledge that " Sadly that's a minority of applications " . It is an " abuse" and should be [happy] " that's a minority of applications" when corrected. You have your right to insist on your preference/opinion.
Che Kuan Yau (Singapore)

 

[davidbeach]

You always need to separate out normal stop from the "oh sh!t" stop. Normal stop can be reset at will by whom ever. The "oh sh!t" stop has a full procedure to go from stop to run again. In my world it's the difference between tripping a breaker and tripping a lockout relay that both trips the breaker and blocks its close. Heck, the breaker may even auto reclose, but that lockout relay demands that someone evaluate the situation. Routine use of a lockout would certainly provide a regular test of its functionality but it would also remove the "oh sh!t" aspect and sometime somebody would reset it when that would be a very bad thing.

 

[controlsdude]

Start/Stop station usually found at main control enclosure or HMI central display (control room). Start/start can be a real button or a button on an HMI display.

Estops located at any operator interface where the operator is interacting to the machine.
If you have an estop usually there is a reset button located next to the estop. The reset will usually restart/reset the system after the emergency stop was pushed. Hitting estops for some regular stop should not be used in these areas since emergency is just that an emergency and should be treated as such.

Emergency Stop areas are usually defined by safety committees in that industry or that plant. Safety committees usually will define the above requirements.

A safety committee is usually made up of maintenance, plant manager, operations manager, HR, and maybe a industry representive.

There is safety standards that exist in controls and these have evolved from 2 standards in past 30 years. ASTM and ANSI standards have combined these to put forth a standard face to safety. This is where risk assessments are generated from and there is some courses given by control manufacturers that represent these requirments. I think its called TUV, SUV (another TLA)

https://www.tuvsud.com

https://www.bing.com/videos/search?q=risk+assessment+matrix&qpvt=risk+assessment+matrix&FORM=VDRE